This invention relates to a method for presetting a machine, such as a printing press, which produces multiple copies of a product which are judged as to acceptability at least in part by subjective operator evaluation.
This invention has application to any machine or process wherein an objective standard may be used initially in presetting the machine, and wherein the machine output can thereafter be varied or adjusted in accordance with a subjective determination by its operator.
A typical example is in the setting of each of the ink fountains on a printing press. Each fountain is provided with a plurality of keys, all of which are adjusted prior to printing, to meter the amount of ink flowing onto the printing plate. In manually operated presses, the pressman will first scan visually the printing plate and estimate the amount of ink needed within each of the sections controlled by the keys of the ink fountain. There are other systems wherein an optical scanner is used to scan a printing plate to determine the amount of ink needed within certain narrow sections of the printing plate, and that information is then processed to set automatically the corresponding keys of each fountain.
Many modern day presses are provided with electromechanical means for setting the keys from a remote location, and also transducers for indicating each key position at a remote location, for example, on a television screen. Also, means may be provided to record the information from the optical scanner regarding the percentage of coverage on the printing plate for each key position. Key position and other press information deemed by the pressman to represent the best printing quality is recorded so that, if the printing run were interrupted, for whatever reason, that information could then be recalled and used to preset the machine when printing is resumed using those same plates.
Previously, the keys of the fountain were preset either according to the judgment of the pressman or by automatic means as described above. Once these initial adjustments were made, the press was then started and further adjustments made to the fountains and other systems, such as to compensate for registration of various colors, water fountains, etc., to improve the quality of the output until it achieved acceptable quality, known as "save" quality. As the press continued to run, still further fine adjustments were made by the pressman until, usually after several hours of running, a quality of printing of high grade results, known as "OK" quality. It is the "OK" quality settings that are recorded for later use should the printing operation be interrupted, for example by a priority printing job, during the middle of a run.
Information from a plurality of previously completed jobs, including data obtained from an objective source and data obtained from a subjective source, are analyzed and compared to provide parameters which thereafter are used in setting machine functions in response to subsequently obtained objective data.
Specifically, the objective data, such as the amount of coverage as determined by the optical scanner, for each of the elements to be controlled, such as keys, is analyzed mathematically, and a Fourier analysis is made to derive amplitude information for a plurality of harmonics sufficient to represent accurately the relationship between the objective data and the element to be controlled.
Similarly, the subjective data, such as setting as determined by the pressman for the "OK" condition, for each of the machine elements to be controlled, such as keys, is also analyzed mathematically and represented by a plurality of amplitude values for a sufficient number of harmonics to represent accurately the above mentioned relationship.
In presetting the ink fountains of printing presses, it has been found that an analysis of only the first four harmonics of the above information will provide accurate information, as disclosed in copending application Ser. No. 51,930, filed June 25, 1979. Preferably, the average or zero harmonic is taken, and the sine and cosine functions of the first, second, third and fourth harmonics analyzed.
For each of the above nine analysis, derived from a Fourier analysis of each of the waveforms for the objective data and the subjective data, i.e., the percent coverage versus key number and key setting versus key number representations, an amplitude value is obtained. Therefore, for each of the nine analysis, for each job, there will be a single point representing the relationship between objective data (percent coverage) and subjective data (key setting). The data points for all jobs for each of the nine analysis are then plotted, and both the slope and the offset of these relationships are found by the least squares method. This information is then used to predict the key settings likely to be made by an operator on a particular press when a new set of objectively derived data is obtained.
When the method described above was first proposed, it had been assumed that the parameter identifier would be more or less traditional, based on statistical evaluation of adaptive parameters for at least 10 recent jobs, and that updating of parameters would be made not very often, at least every several months. But experience made it clear that the control strategy should be much more complex.
First of all, many jobs, with so-called "bad plates" or "dead alleys," didn't fit any adaptation at all and had to be ignored when they appeared. On the other hand, blown-up ink rolls or unscheduled maintenances appeared quite often; they changed inker's parameters drastically; and therefore they required ignoring the previous information and starting the adaptation anew.
From our human experience, it seems to be simple to ignore something (or someone), but this is not true with automatic systems: they are objective, and therefore they need a reason for ignoring; so both a concept, and a method, and criteria for acceptance/rejection must be developed. These items appeared to be not trivial. Not only was a decision-making procedure in the adaptive controls not available in the prior art, but the existing philosophy of adaptive control could not be applied.
For example, if one tried to apply the well-established notion of running averages (or cumulative sums, or stochastic approximation), failure would result. In a process of adaptation, the established majority (a "mafia-like family") will test every newcoming job for fitness, and the "family" will reject those newcomers on a one-by-one basis even if the newcomers as a group present a new majority, i.e., even if they present an objective change in press condition that should be adapted. Hence, using the traditional statistical adaptation procedure for the acceptance test purposes makes the adaptation itself impossible.
Other pitfalls that had to be avoided are: (1) "Adaptation by default" due to not assured redundancy (two-job adaptation), or not assured alternative adaptation for rejected jobs, etc.; (2) r.m.s. adaptation error as a criterion; and (3) saving jobs for adaptation on a job, not a fountain-basis.